This invention relates in general to sewing machines and in particular to a new and useful drive for a presser foot which makes it possible to drive it in a plurality of vertically different operating ranges.
A presser foot device similar to the present invention is described in German OS No. 25 07 544. The swingingly driven presser bar has attached to it a projection with which each downward stroke impinges on an abutment element. Through a second compressed air cylinder, the abutment element can be moved between two different height positions, whereby the lower dead center of the oscillation of the foot can be adapted to different sewing conditions as for instance work thickness, type of stitch formation, etc. However, when raising the abutment element only the lower dead center of the oscillation of the foot is displaced and thus the swinging range of the foot is narrowed. Therefore the known presser foot device is suitable only for limited height adaptations.
For some sewing jobs, e.g. in shoe manufacture, there occur during the sewing at cross seams and at transition points of overlapping work parts such different work thicknesses that a two-step adjustment of the lower dead center of the foot is too imprecise. Since the downward movement of the presser bar is decelerated abruptly when the projection strikes the abutment element and therefore great impact forces occur, the known presser device can further be used only for slow running sewing machines.